1. Field of the Invention
The present invention relates to an automatic color saturation controller incorporated with a color demodulator for a color TV set, and more specifically to an automatic color saturation controller for simultaneously providing a higher killer sensitivity and a higher chrominance signal quality.
2. Description of the Prior Art
In a color TV set, an automatic color saturation controller (referred to as ACC hereinafter) is incorporated to maintain the color saturation (an attribute representative of color density expressed by a mixture ratio of monochrome to achromatic color) of a reproduced color video signal at a constant level against the input level fluctuations of chrominance and luminance signals, by controlling the amplitude of the chrominance signal. Conventionally, a peak detector ACC and a synchronous detector ACC are both well known as the above ACCs. In the peak detector ACC, the peak value of color burst signal is detected to adjust a gain controller for the chrominance signal. In the synchronous detector ACC, the color burst signal is detected in synchronism with the reference chrominance subcarrier to adjust a gain controller for the chrominance signal.
In the case of the peak detector ACC, however, there exists a problem in that the output of the gain controller is excessively reduced when field strength is weak and therefore the S/N ratio of the color burst signal is lowered, so that a color killer circuit is erroneously activated to change the color TV broadcasting to a monochrome TV broadcasting (because the absence of color burst is detected), that is, the killer sensitivity is degraded at a weak field strength.
On the other hand, in the case of the synchronous detector ACC, there exists another problem such that when field strength is strong and further the S/N ratio of the color burst signal is lowered, it is difficult to stably maintain the amplitude of the chrominance signal at a constant level, because the color burst signal is detected without being subjected to the influence of noise included in the burst signal, so that the chrominance signal stability is degraded at a strong field strength.
The characteristics of the peak and synchronous detector ACCs will be described in greater detail hereinafter with reference to the attached drawings under DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT.